I had a noisy varactor experience too: in my Tek 492 one day I noticed an increase in the 0 beat noise and the PLL not working. When I replaced the 2.2GHz conversion varactor all was back to normal.
On Fri, Oct 19, 2012 at 6:54 AM, Tom Curlee <[email protected]> wrote: > I'll second the interesting part. > > I have a problem with a 10 GHz brick oscillator LO that I converted to GPS > lock. I don't remember the instantaneous frequency jumps (around 200 - 400 > HZ at 10 GHz) before I did the GPS lock (although it's possible). Please > note that this is NOT any type of GPS phase shift. I built a extremely > slow frequency lock circuit that has a loop time in seconds. The jump is > instantaneous and I can then see the control voltage slowly change to > correct the error. When the frequency jumps back, the control voltage > slowly follows. Since this brick has the usual 106.5 MHz crystal > (multiplied by 96 to get 10.224 GHz for the LO), I'm seeing at most 400 HZ > / 96 shift in the crystal oscillator. > > I've wondered if I have a noisy varactor diode. The diode selected was > one I had around, selected only because it had a low-ish capacitance > value. I haven't gotten around to digging into the problem any farther. > > Anyone have any more info or ideas? > > 73, > > Tom WB6UZZ > > --- On Thu, 10/18/12, John Miles <[email protected]> wrote: > > From: John Miles <[email protected]> > Subject: Re: [time-nuts] HP 10811 Tuning Diode > To: "'Discussion of precise time and frequency measurement'" < > [email protected]> > Date: Thursday, October 18, 2012, 8:54 PM > > That's extremely interesting, Adrian. I've never heard of a noisy > varactor, > but then I've never looked for one, either. It'd be great if some of the > problems that have been blamed on jumping crystals were in fact caused by > the tuning diode. What steps did you take to rule out the crystal and > narrow down the problem to the diode? > > -- john, KE5FX > Miles Design LLC > > > -----Original Message----- > > From: [email protected] [mailto:time-nuts- > > [email protected]] On Behalf Of Adrian > > Sent: Thursday, October 18, 2012 12:19 PM > > To: Discussion of precise time and frequency measurement > > Subject: [time-nuts] HP 10811 Tuning Diode > > > > Hello, > > > > I found the 10811 in my 8662A to be quite noisy and was able to trace > > the problem down to the tuning diode. > > Actually, the phase noise started to jump when the oven heated up. As a > > quick solution, I replaced it with a SMD type that I had at hands. > > > > I would appreciate any hint where to find an original diode (even though > > I could leave it as is). > > > > As by the manual, the original is a '0122-0244 DIODE-VVC 100PF 5% > > C4/C25-MIN=2 BVR-30V Mfr. 28480' > > Mfr. 28480 is listed as HP, but the diode is marked 'M' for Motorola and > > '0244' and '312'. > > > > Adrian > > > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to https://www.febo.com/cgi- > > bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
